In recent years, there have been studied and developed systems for evaluating automobile's performance to protect pedestrians when the vehicle comes into collision with a pedestrian in advanced countries. Head portion is largest in number among body parts on which pedestrians are vitally injured in collision with an automobile. Therefore, also on a method of a head impact test for evaluating the protections of head from impact, international standards (ISO/SC 10/WG 2) and EU standards (EEVC/WG 10, ECE-Regulation No. 43 Annex 3) are defined.
For example, European Enhanced Vehicle-safety Committee; EEVC/WG 17 has proposed a test for the protections of head as a part of a test for the protections of pedestrian and has proposed a condition that a Head Injury Criteria (HIC) value, which is determined by a method according to this test for the protections of head, does not exceed 1,000 as a performance standard on automobile's safety. Further, an HIC value of 1,000 is a threshold of being seriously injured, and it is said that when the HIC value is higher than 1,000, a probability of survival of a normal human being becomes lower.
Front noses of recent automobiles have tendencies to be shortened and in the recent accidents, a location of vehicles with which the head of an adult pedestrian comes into collision is often a windshield other than a hood.
But, since the test for the protections of head of EEVC/WG 17 limits the scope of test to on the hood of the passenger cars by its definition, in the ongoing International Harmonized Research Activities (IHRA), it is considered to include the windshield in the scope of the test for the protections of adult head.
Currently, as the glass for vehicles such as automobiles, aircrafts, buildings and the like, laminated glasses are widely employed because less fragments of broken glass shatter even though the laminated glass is impacted externally and broken and therefore the laminated glass is safe. As such a laminated glass, there is given a laminated glass obtained by interposing an interlayer film for laminated glasses, which comprises polyvinyl acetal resin such as polyvinyl butyral resin plasticized with a plasticizer, between at least a pair of glass sheets and unifying them and the like.
However, many of conventional laminated glasses have the HIC value of higher than 1,000. Especially in windshields of automobiles, the HIC value is particularly high in the vicinity of a periphery of the windshield secured to the window's frame and some laminated glasses have an HIC value of higher than 2,000. Such the vicinity of the periphery of the windshield is a location with which the head of an adult pedestrian comes into collision at a high probability in the occurrence of an accident, and a laminated glass having a lower HIC value has been required in order to avoid damages to head in the collision of pedestrian with vehicles.